Dispenser cathodes are also called matrix cathodes. They consist, in general, of a dispensing body, which is pressed or sintered from a metal powder and is impregnated with the actual emission material. Metals such as tungsten, molybdenum, or chromium can be considered for use as the metal powder for the dispensing body. The use of mixtures of such metal powders has been known as well. It has been known from, e.g., German Auslegeschrift No. DE-AS 10,68,818 that the dispensing body can be built up in a layered pattern. It has been known from German Offenlegungsschrift No. DE-OS 20,48,224 that dispensing bodies can be pressed into a cavity of a cathode sleeve. The porous matrix body can be impregnated with an emission material, which consists of, e.g., BaO-CaO-Al.sub.2 O.sub.3, by impregnation, melting in, or the like.
It has been found, in general, that so-called mixed metal cathodes, i.e., cathodes whose dispensing bodies are pressed and sintered from a metal powder mixture, posses improved emission properties and better current stability. The dispensing bodies of mixed metal cathodes consist, in general, of metals of a first group, such as tungsten, molybdenum, or chromium, and of metals of a second group, such as nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pd), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), scandium (Sc), yttrium (Y), lanthanum (La), lanthanides, titanium (Ti), zirconium (Zr), hafnium (Hf), niobium (Nb), and tantalum (Ta). A higher percentage of metals of the second group, especially a higher percentage of Os, was found to have a highly favorable effect on the stability of the emission current. However, shrinkage of the sintered body, as a result of which poor heat transmission to the cathode sleeve and undesirable evaporation of the emission material occur, was found to be disadvantageous.